Tesis doctoral de María Teresa Penella López
Autonomous sensors (as) are wireless measurement units that include sensors and signal conditioners, a processor, a transceiver, and the power supply. In order to save power, they usually remain most of the time in a sleep mode and only wake up to perform some function. The emergence of wireless communication standards and the reduction in the power consumption, cost, and size of the electronic devices have been drivers of the field of as. Still, the power supply and management of the as remain as one of the critical issues for their long-term deployment. two main alternatives are currently being used in order to power as: primary batteries and energy harvesting. In this thesis we provide an integral approach to the power supply of as dealing with batteries, storage units and energy harvesters. We propose circuits and methods for the efficient energy and power management. To limit the number of topics, we only deal, in the topic of energy harvesting, with optical and (deliberately radiated) rf energy. first of all, the power consumption of the as is considered and analyzed, leading to a model that considers the load (as excluding the power supply) as a pulsed current sink. Experimental measurements in a commercial as support the analysis. A general analysis of the ambient energy sources susceptible to be used to power as is also provided. Characteristics such as power density or availability provide essential information for considering their use in as and to design the power supply subsystem. primary and secondary batteries and supercapacitors have been studied and characterized. Secondary batteries and supercapacitors can be used as storage units when harvesting energy but not as the main power source due to their leakage and low energy density, respectively. Some batteries, especially the models with a low capacity, have a relatively high series resistance. When the as wakes up, both a voltage drop and power dissipation are generated in the battery resistance, shortening the lifetime of the as. In order to overcome these issues, we propose the use of hybrid storage units formed by a battery in parallel with a supercapacitor. We show that supercapacitors extend the battery lifetime between 16 % and 33 % when powering as. a generic model for optical energy transducers (solar cells) has been used to compute the i-v and p-v curves and their dependency with optical power and temperature. Then, we consider methods and circuits for the efficient energy management with different circuit implementation complexities. We first analyze the performance of a direct-coupled (diode) connection leading to efficiencies between 70 % and 90 %. Then, we propose maximum power point tracking (mppt) methods. First, we show a new implementation of the focv method, which leads to a tracking efficiency higher than 99.5 %, higher than that reported by current implementations. Additionally, a new mppt method is reported and tested, achieving a tracking efficiency higher than 99.6 % and an overall efficiency higher than 92 % for a pv panel power higher than 100 mw. Outdoor field measurements show energy gains around 10 % compared to a direct-coupled solution. finally, the rf energy transducer (antenna) is analyzed for its use in as. Based on circuits proposed in the literature, we perform extensive simulations for several incoming power levels at the antenna (from -10 dbm to 10 dbm). Circuit efficiency slightly depends on the number of stages used for the voltage rectifier multiplier but shows a large variation with the received power, ranging from 80 % at 10 dbm to 10 % at -10 dbm. Graphs of the efficiency versus the output voltage of the rectifier are shown at several power levels and number of stages of the circuit rectifier. As the power level increases the output voltage at which the efficiency is maximum increases. Experimental tests with a folded dipole antenna and a three-stage rectifier are also shown.
Datos académicos de la tesis doctoral «Methods and circuits for the efficient management of power and energy in autonomous sensors«
- Título de la tesis: Methods and circuits for the efficient management of power and energy in autonomous sensors
- Autor: María Teresa Penella López
- Universidad: Politécnica de catalunya
- Fecha de lectura de la tesis: 27/09/2010
Dirección y tribunal
- Director de la tesis
- Manuel Gasulla Forner
- Tribunal
- Presidente del tribunal: gerard c.m. Meijer
- vittorio Ferrari (vocal)
- (vocal)
- (vocal)